    Patent Document 1: Japanese Unexamined Patent Publication (Kokai) No. 2002-159866    Patent Document 2: Japanese Patent Gazette No. 3350691
Polymer Electrolyte Fuel Cells (PEFCs) are devices, which are capable of directly converting chemical energy into electrical energy, starting from room temperature, being downsized and lightened; and are expected to be used as new energy sources for such applications as co-generation for households and automobiles. Among the methods for supplying hydrogen, the fuel necessary for PEFCs, hydrocarbon reforming is considered to be the easiest approach considering the infrastructure development; however, the Pt catalysts on the PEFC anodes adsorb the CO in the reformed gas, or are poisoned by the gas, and are deactivated, making their practical applications difficult.
In addition, gases other than CO, such as H2S, SO4 and HCHO, are suspected to lower the catalyst's capabilities. As a countermeasure, Pt—Ru alloys are currently used as catalysts with a tolerance to CO poisoning (Patent document 1). However, Ru is a rare metal and is anticipated to become a huge bottleneck in the future progress of the PEFCs because of risks, such as a steep rise of its price. Therefore, one of the most important issues, in the development of PEFCs, is to develop a catalyst with a tolerance to CO poisoning, which takes the place of the Pt—Ru (Patent document 1).
As a technology for a catalyst with a tolerance to CO poisoning, a technology for surface treatment (fluorination) of a hydrogen absorbing alloy is described in Patent Document 2. The fluorination inhibits a LaNi5 hydrogen absorbing alloy, which, as in the case of PEFC anodes, suffers from being deactivated by CO adsorption, from being poisoned with CO, in this case, by having fluorine adsorbed on the catalyst's surface either from a diluted fluorine gas, or from hydrogen fluoride; the fluorination inhibits the catalyst from being poisoned with CO. Because the method is featured by a capability of changing the catalyst's characteristics after the preparation of the catalyst, a capability which did not exist in the conventional catalyst preparation methods, the method is expected to provide, if brought into practice, an easy-to-use inexpensive catalyst preparation.
However, the technology described in the Patent Document 2 involves forming a film, mainly comprising a metal fluoride, on a hydrogen absorbing alloy; but metal fluorides do not necessarily inhibit other metals, or other alloys, from being poisoned with CO.
Furthermore, there is a need for a material excellent not only in a tolerance to CO poisoning, but also in tolerances to H2S poisoning, SO4 poisoning and HCHO poisoning.